Generation of polyphase alternating electric currents of varying frequencies.



W. P. DURTNALL. GENERATION or PoLYPHAsB ALTERNATING ELECTRIC GURRBNTS oFVARYING PRBQUENGIBS. APPLICATION FILED NOV. 1, 1909.. 1 ,098,345,Patented May 26, 1914.

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UNITE STATES PATENT ltltlltlltll@ WILLIAM PETER DURTNALL, GF HERNE BAY,ENGLAND.

GENERATION OF POLYPHASE- AL' llEIwll'A'llNG` ELECTRIC CURRENTS OFVARYING FREQUENCIES.

T0 all fro/om 'it may concern:

Be it known that I, YILLIAM Pnrnn BURT- NALL, a subject of the King ofGreat Britain, residing at Herne Bay, T`ent, England, have invented newand useful Improvements 1n the Generation of Polyphase AlternatingElectric Currents of Varying Frequencies, of which the following is aspecification.

This invention relates to the generation of polyphase. alternatingelectric currents of v-'arying frequencies, thereby providing speedregulation for the motor or motors of any vessel, locomotive, vehicle,or other apparatus which derives its po-wer from such currents.

By the said invention, it is possible where necessary to obtainincreased torques and slower speeds relatively to those of the primemover', or slower speeds and lower powers of the motor or motorsv forany lower vessel, locomotive or vehicle speeds.

In the accompanying drawings, have shown how my said invention may beconveniently and advantageously carried into practice. l

n these drawings, Figure l is a diagram of an arrangement for drivingone or more of the axles of each of the vehicles in a railor road-trainand for obtaining high-starting torques, and Fig. 2 is an end view oftheV brake mechanism of the alternator in this plant.

A multiple pole electro-magnet B is mounted on the shaft A which may bedriven by a suitable prime-mover such as a steam turbine or an internalcombustion engine which may run at a constant speed together with therotor H of a machine which may be termed al transfcrmer-generator. Theseparts B, H revolve and at the same speed. rFhe multiple-pole magnet B isexcited through slip-rings D, D from a continuouscurrent exciter E,which is preferably serieswound and is adapted to have its field-magnetor magnets E short-circuited by means of a switch'F. An armature orstator C is mounted outside t-he multiple pole magnet B and providespolyphase alternating current of a certain periodicity, which can beeither sent direct to the stator L of the induction motor or motors, therotor K of which will then run at a certain speed, or the abovepolyphase alternating current may be connected to the primary of thetransformer- Specicaton of Letters Patent.

Application filed November l, 1909.

Patented May 26, 11.314. Serial No. 525,735.

generator. In the example shown, the rotor H is wound as the primary,the connection being made through slip-rings G, G in such a manner thatthe resultant magnetic flux revolves at the air gap in a directionopposite to that of the mechanical rotation (at say one-third, or othersuitable fraction of the mechanical rotation speed) the current sogenerated can then be drawn olf from the secondary or stator l of thetransformergenerator at a periodicity which is variable according to thenumber of poles in the rotor and stator of the saidtransformer-generator, and in the rotor and stator of the polyphasealternating current generator B, C, as described above (the generatormay have more or less poles than the transformergenerator, accordinglyas it is desired that the said generator B C shall supply current ofintermediate or minimum periodicity). The current from the secondary lcan be then taken direct to the stator L of the motor or motors, whichwill then run at a speed set by the periodicity of the polyphasealternating current delivered thereto.

Now in order to get a higher speed from the motor or motors, and also ifnecessary to enable more power to be taken therefrom, two of the phases(if three-phase current) of the connections between the armature C ofthe alternator and the rotor H of the transformer-generator can bereversed, so that the currents then flow in the opposite direction andthe resultant magnetic flux at the air gap of the transformer generatorrevolves in the same direction as, but at say one-third, or othersuitable speed ahead of the mechanical rotation of the primary of thetransformer generator, therefore current can then be taken from thesecondary of the transformer generator, at higher periodicity andvoltage and consequently power, as part of the power from theprime-mover is delivered to the polyphase alternating current generator,and is converted into electrical energy, which being put into therevolving primary H of the transformer-generator, acts to excite thesame as a held-magnet of a generator, the armature of which is thestator I, and this transformeregenerator absorbs a further amount of themechanical power of the prime-mover, which is converted into electricalenergy in the secondary winding I of the transformer generator, to

which is added the energy due to the rotation of the magnetic field onthe rotor H produced by the polyphase current coming from the polyphasealternating current generator, so that the total power of the primemover(minus the ordinary losses) may be represented in electrical energy atthe terminals of the secondary I of the transformer generator. If it bedesired still further to vary the periodicity, voltage and power asdelivered to the motor or motors, the armature C of the generator may bemounted on bearings R, B, with the necessary slip-rings S, S, S to takethe current off, so that it may if necessary revolve in the samedirection to the multiple magnet B. By arranging a suitable brakingarrangement, c. g. the band T and tighteninglever U (which is shown inthe normal position with the armature stationary), the armature C maybek allowed to rotate at any speed intermediate of zero and that of thefield magnet B and in the saine direction as the latter. By letting thearmature C slip freely in the band T, it will ultimately run at the samespeed as the multiple magnet B,when the periodicity of the whole systemwill have fallen to zero. 0nl the other hand, by driving the armature Gin the opposite direction to the field magnet, the periodicity andvoltage may be increased. By applying a generating plant such as thoseabove described to a motor or motors with a single winding on itsstator, three set speeds may be obtained with a squirrel-cage rotor orrotors; if necessary a higher speed can be obtained or any intermediatespeed between the three above speeds and zero.

In order to facilitate the change from one speed to another, the Voltageis in each case brought to Zero in the whole system by closing theswitch F before altering the connections, so as to dee'nergize the fieldof the exciter E. Vhen the change is made, the switch F is opened, thevoltage will rise again and the motor run at the new speed.

The current of different periodicities is shown supplied to a pluralityof motors L, L2, L3 each driving one of the axles V of a railorroadtrain. By this arrangement, high initial torque can be obtained, forinstance, when it is desired to start the train on an upgrade, since itis a well known fact that induction motors have a high torque whensupplied with current of a lower frequency than the normal. Thus, theacceleration or retardation of the train can be efficiently controlledentirely by means of the brake T, U. Here the reversal of the twophase-connections between the slip-rings S and G is effected by means ofa reversing switch 2, and the connection of the motors L, L, L, toeither the alternator armature C or the secondary I of thetransformer-generatorby means of a S-pole 2-way switch 1,

these switches 1, 2, each having an intermediate position in which thealternative circuits are both open.

The following specific example may be given of the operation of plantssuch as those illustrated: A steam turbine drives the shaft A at 1,000R. P. M., the alternator B, C being a four-pole separately-excitedthreephase machine. On the shaft A is also mounted the primary H of atwelve-pole transformer-generator, the secondary member I of whichremains stationary. The electrical energy from the above combination isreceived by a one hundred-pole squirrel-cage polyphase alternatingcurrent induction-motor coupled e. g. to a ships propeller shaft. Theoperation of the above plant, when the connections are as indicated inFig; 1, will be as followsc-Since the turbine speed equals 1,000 It. P.M., and the alternator has four poles, the current from said alternatorwill be of 4,000 alternations (half-periods) per minute, and thiscurrent when applied to the above motor, will give the latter asynchronous speed of 40 R. I). M. If now the alternator be disconnectedfrom the motor, and the current be sent instead into the revolvingprimary H of the transformer-generator, in such a direction that themagnet-ic flux revolves in the primary H in the opposite direction tothat in which the latter is being driven by the prime mover, the currentbeing taken to the windings in the primary by means of the sliprings G,and brush-gear, the resultant periodic-ity in the fixed secondary I willbe as follows:-Taking the periodicity of the alternator-current again at4000 alternations per minute and taking the speed of the primary of thetransformer-generator at 1000 B. P. M., with 12 poles, the current inthe secondary I will be of a periodicity ofV 12,000 minus 4000alternations per minute due to the backward rotation of the magneticfield on the rotor, that is to say there will be 8000 alternations perminute in the secondary I of the transformer-generator and by taking thecurrent from this secondary to the above motor the resultant synchronousspeed of the motor or propeller shaft will be R. I). M., and ifnecessary higher voltage and therefore more power. Now disconnect thecurrent from the generator C to the primary slip-rings G, reverse two ofthe phases of the in-going threephase current from the generator C tothe primary H of the transformer-generator, reconnect, and the resultantconditions will be as follows: Taking the periodicity of thealternator-current again at 4000 alternations per minute, then since thespeed of the transformergenerator primary H is 1000 R. I. M., with 12poles, the current in the secondary I will be of a periodicity of 12000plus 4000 alternations per minute, that is to say 16000 alternations perminute in the secondary of the transformergenerator, then by taking thissecondary current to the above motor, the synchronous speed of the motoror propeller shaft, will be 160 revolutions per minute, if necessary athigher voltage and therefore more power. lt will thus be seen that, inthe above quoted case, three set speeds may be procured on asinglestator-winding squirrel-cage induction polyphase-current motor, orby enabling the armature of the four-pole generator to rotate as abovedescribed, the periodicity and consequent voltage of the whole systemmay be varied to any desired degree, and the speed of the saidone-hundred-pole motor with it, and with good mechanical efliciency, anda minimum of electrical losses. The above motor or motors may be coupledto a ships propeller shaft or shafts, or to the axle or axles of avehicle, locomotive, train or the like, as the case may be, in the mostsuitable manner in order that in the case of the locomotive or train thefull weight, (or as may be arranged for) of the train or locomotive andthe like may be utilized for tractive effort, braking and powerdistribution.

By arranging the connections through suitable switch-gear, as shown forexample at 2', a full power reverse direction of speed can be given tothe above motor or motors, this being effected by reversing two out ofsay three phases of the current at the terminals of the motor or motorswithout alternating the speed or direction of rotation of the primemover.

A fourth speed can be obtained by supplying direct current to two of thesliprings G of the rotor of the transformergenerator. This can beobtained from the exciter E by means of a switch V, the said exciterbeing meanwhile disconnected from the slip-rings D by means of a switchX. The spe-ed of the rotor K of the motor will then be asfollows:-Taking the common speed of the prime mover, shaft A, andprimary H at 1000 R. P. M., and since the said primary has twelve poles,the periodicity of the current supplied to the motorstator L will be12,000 alternations per minute. Since, moreover, the motor-stator hasone hundred poles, the speed of the rotor of this motor when running atsynchronism will be 120 B. P. M.

lVhen it is desired to run the motor-shaft or shafts at a high speed,the starting is preferably effected at the lowest or at one of the lowerspeeds, the speed being brought up gradually by passing from one speedto another by either of the methods above described. This is renderednecessary by reason of the difficulty which exists of starting inductionmotors by means of currents of periodicities corresponding to theirnormal speeds.

By the above arrangements, a large saving of ste-am can be made ascompared with the existing' steam turbine driven ships, and in vehicles,locomotives and the like so tted, and in cases of application ofinternal combustion engines, a reverse motion can be etliciently givento the driven shafts or axles, and a very powerful braking effectprovided on vessels, vehicles, locomotives, trains and the like, withoutatfecting the prime-mover as regards speed or direction of rotation.rllhe above. makes a very efficient electrical speed reduction and powertransmission gear, and thus provides what is so much desired for marinepropulsion, road traction and the lik z'. c. a high speed, economical,light-weight prime-mover, and slow speed eiiicient propeller orpropellers, axles and the like.

By the arrangement above described, any desired number of inductionmotors can be run at any one of a considerable number of speeds ineither direction as desired.

I claim l. A plant for the generation of polyphase electric currents ofvarying periodicity for a. constant spe-ed of the prime mover, saidplantcomprising a prime mover, a polyphase alternator, a polyphasetransformer-generator comprising a rotor and a stator, a mechanicaldriving connection between said prime mover, the rotary member of saidalternator, and the rotor of said transformer-generator, and electricalconnections between said alternator and the primary of saidtransformer-generator, said connections including means forinterchanging two of the phases of the circuit between said alternatorand said transformer-generator, for the purpose specified.

2. A plant for the generation of polyphase electric currents of varying'periodicity for a constant speed of the prime mover, said plantcomprising a prime mover, a polyphase alternator, a polyphasetransformergenerator comprising a rotor and a stator, a mechanicaldriving connection between said prime mover, the rotary member of saidalternator, and the rotor of said transformer-generator, means forgenerating direct current combined with said alternator, electricalconnections between said alternator and said transformer-generator, saidconnections including means for interchanging two of the phases of thecircuit between said alternator and said transformer-generator and forconnecting said direct current generating means with two of the pbaseconnections of the primary of' said transformer-generator.

3. A plant for the generation of polyphase electric currents of varyingperiodicity for a constant speed of the prime mover, said plantcomprising a prime mover, a polyphase alternator, means for permittingthe rotation of the normally non-rotating member of said alternator,means for controlling the rotation of said normally non-rotating member,a polyphase transformer-generator comprising a rotor and a stator, amechanical connection between said prime mover, the rotary member ofsaid alternator and the rotor of said transformer-generator, andelectrical connections between said alternator and the primary of saidtransformergenerator, said connections including means for interchangingtwo of the phases of the circuit between said alternator and saidtransformer generator, for the purpose specified.

4. A plant for the generation of polyphase electric currents of varyingperiodicity for a constant speed of the prime mover, said i plantcomprising a prime mover, a polyphase alternator, a polyphasetransformergenerator comprising a rotor and a stator, a mechanicaldriving connection between said prime mover, the rotary member of saidalternatorJ and the rotor of said transformer-generator, means forgenerating direct current combined with said alternatorj electricalconnections between said alternator and said transformer-generator, saidconnections including means for interchanging two of the phases of thecircuit between said alternator and said transformer-generator and forconnecting said direct current generating means with the primary of saidtransformer-generator.

WILLIAM PETER DU RTNALL.

lVitnesses:

THOMAS A. BAILEY, H. D. JAMESON.

Copies of this patent may be obtained for ve cents each, by addressingthe Commissioner of Patents Washington, D. C.

